Bump sphinx-book-theme from 1.1.2 to 1.1.3 in the pip group (#265)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Tetsuo Koyama <tkoyama010@gmail.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,3 +1,3 @@
 myst-parser==3.0.1
 sphinx==7.3.7
-sphinx-book-theme==1.1.2
+sphinx-book-theme==1.1.3